In recent years, rechargeable and dischargeable electric storage devices such as battery cells (e.g., a lithium ion battery cell and a nickel-metal hydride battery cell) and capacitors (e.g., an electric double layer capacitor) have been adopted as the power sources of vehicles (e.g., an automobile and a motorcycle) and various devices (e.g., a portable terminal and a laptop computer). For example, various energy-dense lithium secondary battery cells are made available as a power source for electric vehicles or the like. A lithium secondary battery cell includes an electrode assembly housed in a metal case, electrode terminals projecting from inside the case to the outside of the case, a current collector which interconnects the electrode assembly and electrode terminals, and an insulating cover disposed between the case and the electrode assembly to insulate them.
Patent Document 1 (JP-A-2009-26704) describes a battery cell including an electrode assembly (“electrode element” in Patent Document 1) designed to be easily insertable into a case (“outer case” in Patent Document 1) and an insulating cover (“insulating film” in Patent Document 1). In the battery cell, the electrode assembly 120 is inserted in the insulating cover 110 having the shape of a bag with an opening 111, is then placed in an interior space 131 formed in the case 130 and is supported by the inner walls of the case 130 via the insulating cover 110 as illustrated in FIG. 7.
Projecting sides 112, 112 are formed at both sides of the insulating cover 110 by pressing both sides of the insulating cover 110 from two sides to integrate them together. Accordingly, the two projecting sides 112 of the insulating cover 110 come into contact with the inner walls of the case 130. This reduces friction resistance caused when the insulating cover 110 is inserted into the case 130.
In the battery cell described in Patent Document 1, spaces as wide as the widths of the projecting sides 112 are formed inside the case 130 by the provision of the projecting sides 112 of the insulating cover 110. Furthermore, the spaces are formed to be longer than the projecting sides 112 so that the lower edges of the projecting sides 112 do not hit the inner walls of the case 130 when the electrode assembly 120 housed in the insulating cover 110 is inserted into the case 130.
Accordingly, in the battery cell described in Patent Document 1 described above, the electrode assembly 120 is not positioned in place inside the case 130 simply by inserting the electrode assembly 120 into the case 130. Consequently, the electrode assembly 120 can tilt so that the front and rear surfaces are at an angle with respect to the front and rear surfaces of the case 130. In that case, the cover plate of the case 130 to which the electrode assembly 120 is attached through the current collector does not fit the opening of the case body of the case 130. Accordingly, attaching the cover plate to the opening of the case body of the case 130 becomes considerably troublesome. This problem can occur with a capacitor (such as an electric double layer capacitor) as well.